Fluids produced from oil wells penetrating an oil-bearing formation primarily include crude oil and water and are herein referred to as formation fluids. A formation fluid may also contain natural gas and natural gas condensate which may or may not be desirable and may be the primary product of a given well in which case the well is referred to as a gas/gas condensate well. A formation fluid may also contain carbon dioxide (CO2) and insoluble clay and silica particles from the reservoir. Contained within the formation fluids are components that under certain conditions can precipitate and impede the production of oil and gas. These components include paraffin and asphaltenes from crude oils and gas condensates and inorganic mineral scales from formation water. Paraffin is a hydrocarbon compound that can precipitate or deposit on production components as a result of the changing temperatures and pressures within the production system. Paraffin may precipitate and deposit as waxy substances that may build up, and if severe, may restrict production and can also gel crude oil. Asphaltenes are organic materials consisting of aromatic and naphthenic ring compounds that may contain nitrogen, sulfur and oxygen molecules; the asphaltene fraction of crude may be understood as an organic part of the oil that is not soluble in straight-chain solvents such as n-pentane or n-heptane.
It is known in the art of oil and gas production to eliminate or mitigate the effects of undesirable paraffin, asphaltene, and scale precipitation. For example, to aid oil and gas production, many chemicals, referred herein as “additives”, which include paraffin inhibitors, asphaltene inhibitors, scale inhibitors, and the like, are often injected from a surface source into wells or through flowlines, such as umbilicals, to treat the formation fluids flowing through such wells and flowlines to prevent or control the effects of precipitation of paraffin, asphaltenes, and mineral scale.
These additives can be injected continuously or by batches into wellbores, at wellheads, or other locations in flowlines or pipelines carrying formation fluids. In addition, an additive can be injected into a near wellbore formation via a technique commonly referred to as “squeeze” treatment, from which the additive can be slowly released into the formation fluid. Injection of additives upstream of the problem location is preferred. Sometimes, additives are introduced in connection with electrical submersible pumps, as shown for example in U.S. Pat. No. 4,582,131, or through an auxiliary line associated with a cable used with the electrical submersible pump, such as shown in U.S. Pat. No. 5,528,824. In addition, in wells without a packer in the completion, additives may be applied via pump or truck into the annular space between the tubing and the casing with a fluid flush driving the additive into the formation fluids.
Of the additives that can be added to formation fluid from oil and gas wells, the paraffin inhibitors are especially important. U.S. Pat. No. 4,110,283 to Capelle discloses that a copolymer of 4-vinyl pyridine and acrylic acid esters dispersed in an aqueous medium can prevent the deposit of solid paraffin on the walls of containers and pipelines carrying oil. U.S. Pat. No. 3,951,161 to Rohrback, et al., discloses a method of using electrical contact resistance to detect the formation of paraffin solids in oil and gas wells. U.S. Pat. No. 4,538,682 to McManus, et al., discloses a method for removing paraffin deposits. All of these patents illustrate the need to control the formation of paraffin deposits.
Paraffin inhibitor additives are typically applied in the form of organic solutions or aqueous microemulsions or admixtures. The use of liquid additives is not without problems. At cold temperatures, such as in cold weather or deepwater subsea locations, the additives may freeze or gel during transportation or use. Stated another way, existing commercial paraffin inhibitors may lose solubility at high pressures and low temperatures. Supplying a source of heat, particularly for deepwater and remote well sites can be a problem. Also, when supplying additives in the form of liquids, any solid active components must be co-shipped in solution. The use of a solvent to form the solution requires that inert or non-active components must be co-shipped with the active components, which increases the cost of shipping.
Besides preventing or inhibiting the deposition of paraffin, additives may be introduced into hydrocarbon fluids to modify the crystal structure of the paraffin to inhibit or prevent paraffin from depositing. In one non-limiting explanation, some additives serve as dispersants to disperse already deposited paraffin, to keep the paraffin in a hydrocarbon fluid from depositing or otherwise combining or agglomerating to cause difficulties. It will be appreciated that the term “hydrocarbon” as used herein is broader than simply to mean organic compounds consisting only of hydrogen and carbon, although those are intended. For instance, “hydrocarbon fluid” as used herein encompasses oil and gas, including crude oil and natural gas. However, “hydrocarbon” as used herein does not encompass polymers unless otherwise noted.
Additionally, it is known to introduce additives to hydrocarbon fluids to modify their pour points. The pour point of a liquid is the lowest temperature at which it will pour or flow under the conditions of interest. For instance, it is a rough indication of the lowest temperature at which oil is readily pumpable. For crude oil, a high pour point is generally associated with a high paraffin content. Thus, it is desirable to include additives that will lower the pour point of crude oil and other hydrocarbon fluids.
It would be desirable in the art of oil and gas production to use paraffin inhibitor compositions that have a higher concentration of active components than conventional paraffin inhibitors. It would be particularly desirable to use such compositions that allow for higher active component concentrations under cold temperatures—that are more soluble at the high pressure and lower temperatures typical for umbilical applications. It would thus be very desirable and important to discover methods and compositions for economically inhibiting or preventing paraffin formation in hydrocarbon fluids, such as formation fluids from an oil well or gas well.